Systems used to store and transport high pressure gases are susceptible to containment leaks. These leaks can be both dangerous and difficult to detect. Detection of small leaks in high pressure pipes and storage devices is compounded when the leak site is in an area which is difficult to access, such as a complicated network of pipes. For example, a high pressure hydrogen leak experienced by the National Aeronautics and Space Administration (NASA) grounded a space shuttle flight. To identify the leak location, ultrasonic leak detection equipment was placed on a pan and tilt stage within the space shuttle aft compartment to allow remotely operated leak searches. This system assisted in leak detection, but did not provide a system for imaging a region where an ultrasonic leak is located.
The size of leaks which need to be detected can be described in SCIMs (standard cubic inches per meter), but are best described as a function of the contained pressure and the leak orifice size. A small orifice combined with a sufficiently high pressure creates a jet-like leak. These jet-type leaks create turbulent pressure variations that can be detected with an ultrasonic transducer. Turbulence in air creates detectable sound in the 40 kHz range, and air coupled ultrasonic transducers can detect this frequency of noise given off by leaks. Hand-held leak locating devices having air coupled ultrasonic transducers can be used to detect leaks. For example, a hand-held leak detector is described in U.S. patent application Ser. No. 08/540,616, entitled "Ultrasonic Leak Detection System", filed on Oct. 17, 1995, incorporated herein by reference. While such systems provide a useful means for detecting ultrasonic leaks, they lack the ability to provide an image of a region containing a leak.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an ultrasonic detection system which produces an ultrasonic image of a region of space so that an ultrasonic leak source can be found from its location in the ultrasonic image.